The thing that immediately sticks out to me is the front cover is crooked. On the back side, there's a few rows of pixels along the top that need to go.
I would probably recommend re-making the back from scratch. Match the colour gradient as best you can, then re-type all the words so they're crystal-clear, Generate a new barcode. Many logos are available in vector form, which will look alot more crisp.
Note, I haven't downloaded the cover to actually look, just my thoughts from the preview-sized one. The front appears at first glance to be pretty crisp, and otherwise good except for being crooked.